I'm a natural childbirth educator who specializes in vegan and vegetarian pregnancies.
I also had a vegan pregnancy and am raising a vegan child. Your wife can easily have a great, healthy pregnancy and birth.
She does need to make sure she gets 80g of protein a day, and drinks half her body weight in oz of water. Lots of snacks, eating before bed is great. I'd suggest a whole food based prenatal vitamin, as well as a B12 supplement. Midwifery care is much more friendly to a plant based diet than a mainstream OB. Feel free to contact me if you or she has any questions.